I (very) recently wrote about Eight Reasons Why You Need a One Page Resume. As an example of how you can cut down your resume, I wanted to provide an illustration of how you can, in fact, fit a lot of content on one page - without making your margins tiny.
Here’s what I manage to fit on one page of my resume (view here):

CUT: College projects. They’re coding projects. I’ve demonstrated that I’m highly technical by having other software engineering positions. It just doesn’t matter any more – particularly as I’m not applying for coding jobs.

CUT: TA / Head TA at Penn for 4 years. While being a TA / Head TA does show some valuable communication and other skills, I have already demonstrated that through other activities (such as being an instructor at UPenn / UW).

CUT: Hobbies. It’s not that no one would care that, say, I enjoy playing squash, but a lot more people will care about almost anything else still on my resume. Any that goes for most people - don’t waste time with your hobbies.

CUT: Advisor to various start-ups. Again, it’s not that it doesn’t matter at all, but it doesn’t matter as much as other stuff.

REDUCED: Microsoft and Apple jobs. Although I’ve already demonstrated technical skills through my position with Google, there is something compelling about the fact that I’ve worked at Microsoft, Apple and Google. I don’t need to spend a ton of time discussing these jobs. Just listing them is enough. I put one bullet under each company, covering four internships total, and that’s enough.